This invention relates to a method and an apparatus for processing matter by hydrothermal reactions, such as rupturing of molecular chains, recombination and decoupling occluded molecules, oxidation and reduction reactions, by holding the matter with water held at temperature above 200xc2x0 C.
In recent years, it has been pointed out that ashes generated from incineration of municipal waste contain substances harmful to humans such as dioxin and others, resulting in demands for treatment processing to deal with such matters. Also, needs are increasing for processing halogen compounds, herbicides, PCB, DDT and other organic halogen compounds contained in pesticides, chemical weapons such as poison gas, explosives, substances with high organic contents unamenable to biological processing, waste water containing matters unamenable to biological processing, compounds that suppresses biological metabolic reactions, and other substances that cannot be discharged or left in the environment.
As a method of treating such substances, expectations are high for hydrothermal reactions that hold the substances with water at temperature above 200xc2x0 C. and perform tasks such as severing of molecular chains, recombination and decoupling occluded molecules, oxidation and reduction reactions. This high expectation is because this type of chemical processing can be carried out in a closed-circuit system and the facility can be relatively small.
Especially, in the so-called super-critical zones, it is known that a medium exists in an unusual middle state that is neither gas nor liquid, and exhibits special physical and chemical properties that can be used to perform various treatments. Here, the super-critical state, when the medium is water, means that the temperature exceeds the critical temperature of 374.15xc2x0 C. and the pressure exceeds the critical pressure of 225.56 atmosphere, and a state near this critical point, such as temperature between 200 and 374.15xc2x0 C. at a pressure exceeding the saturated vapor pressure, is called a sub-critical state. Here, in order to create such state, it is necessary to maintain the pressure of the medium to higher than its vapor pressure to avoid the temperature decrease as a result of heat loss caused by latent heat of vaporization. As an example, a relation between temperature and vapor pressure for water is shown in FIG. 9.
Such hydrothermal reactions are useful not only to decontaminate the substances, but are also useful as a technology for converting organic waste matter to carbon slurry, which can be used as a carbon source for fuel or chemical reactions. The process includes steps of: converting organic matter to water slurry; thermal treatment at a high temperature and high pressure condition; washing and dewatering and increasing the calorific value by separating and concentrating dechlorinated solid carbon and oil.
Typical methods and apparatuses for performing super-critical processing are known wherein such steps are conducted as: charging a waste matter to be processed into a vertical pressure chamber; and creating the super-critical zone in the upper half of the chamber and creating a sub-critical zone in the bottom half of the chamber. In such apparatus, chemical reactions such as oxidation reactions are carried out in the super-critical zone, while solid particles that are present in the waste matter or in the reaction products are separated and absorbed in the slurry at the sub-critical zone. A outlet is provided at the top of the chamber to remove the fluid reaction products of the super-critical state region. This discharge fluid is sent to the next processing station through piping provided with a filter, where solid particles included in the reaction products are removed.
In such apparatus, the pressured matter is charged into the super-critical zone provided at upper region of the chamber through a supply pipe. Oxidation of organic substances such as dioxin are carried out in the super-critical zone, and the fluid layer at the super-critical temperature first flows downward and then flows upward. Therefore, combusted liquid waste is discharged through the pipe at the top of the chamber, but the inorganic substances contained in the charged matter, which do not dissolve in the super-critical zone, are precipitated. These precipitates continue to flow downward, due to momentum and gravity forces, and reach the liquid phase in the sub-critical zone. The liquid phase in the sub-critical zone dissolves organic substances that do not dissolve in the super-critical zone, and forms a slurry which does not dissolve in the super-critical zone. The slurry thus obtained is discharged through a pipe provided at the bottom of the chamber which is in the sub-critical zone.
However, in such conventional technology, because the inside wall of the reaction chamber is exposed to the super-critical temperature and strong oxidation ambient, even expensive material such as Inconel are attacked by corrosion. Also, because of this concern for corrosion, it was not possible to raise the reaction temperature too much. Furthermore, the use of such expensive materials, in a thickness range of several centimeters which is necessary to withstand the high pressure above 225.56 atmosphere, results in a very costly apparatus.
In the case of decomposition of substances like dioxin, that are highly toxic at very small amounts, it was very common to use a second reactor in addition to the main reactor. This is because the super-critical oxidation reaction alone cannot raise the temperature high enough to obtain appropriate reaction rates, resulting in insufficient residence time in the chamber for the reacting substances. Also, if the waste matter contains porous matter, only the surface is reacted but the interior matter may be left unprocessed, so that there is danger of retaining toxic substances in the residues.
Also, because the pressure chamber almost behaves as a complete mixing reactor, there is a possibility of some of the substances to be processed flowing out of the chamber without having been processed. One of the possible methods to prevent this is to increase the flow rate by re-circulating the fluid inside the chamber so that increased inflow can stir and mix the contents of the chamber. Another method is to provide a secondary processing chamber for processing the unreacted substances.
Salts are not dissolved in the super-critical zone and are precipitated, whereas they are dissolved and diluted in the sub-critical zone to be discharged. However, a diffusive boundary region between the super-critical and sub-critical zone is exposed to a severe condition where alternating drying and wetting actions take place, and may grow scales consisting of salts and other retained solid particles in its vicinity. For this reason, the location of the boundary region is periodically moved by adjusting the process, and the grown scales must be removed by stopping the process. Some of the scales are difficult to remove, and may even necessitate disassembling the chamber, especially when the chamber is used for processing municipal waste incineration ashes, which may contain calcium, potassium, sodium, chlorine, and sulfur, very often in concentration as high as 10-20%. As a result, it is expected that the chamber cannot be operated over a prolonged period.
Furthermore, when removing the fluid directly from the super-critical zone of the chamber, precipitated micro-particles of salts and solid particles originally contained in the waste matter may sometimes be carried out together. Therefore, it is necessary to remove the particles at the reaction products in the super-critical state with a filter to prevent corrosion of the delivery pipe. However, because the process temperature exceeds 374.15xc2x0 C., the filter must be made of expensive materials such as ceramics, and often faces clogging problems.
Furthermore, relatively non-fluid substances such as salts and occluded solid particles tend to settle in the bottom of the chamber. To remove such settlings, it is necessary to introduce a carrying fluid medium separately in addition to the original feed water. The result is that the amount of by-products increases, and post-process treatments become overloaded.
Furthermore, when the reaction products are re-circulated, the feed material is diluted with the reaction products, and the feed and reaction products are mixed completely in the super-critical zone, it is not possible to form a localized high-temperature high-speed reaction field, as one in a usual air combusted flame. For overcoming this low temperature, increasing the reaction times is very often required.
The purpose of this invention is to provide a practical method and apparatus for conducting high-temperature hydrothermal reaction for resolving the problems in the conventional technologies outlined above.
This invention relates to a super-critical reaction apparatus for processing a mixture phase, comprising an object matter to be processed and a medium in a liquid form, by subjecting the mixture phase to the super-critical state of the medium. The apparatus has: a reaction chamber of a substantially vertical cylindrical shape with a feed supply inlet at an upper end and a product outlet at a lower end; and an interior section of the reaction chamber comprising the super-critical zone above and a sub-critical zone below, wherein the object matter and reaction products are progressed in one direction towards the lower end.
Accordingly, compared to the case of withdrawing the reaction product in the super-critical state, it is possible to process the waste matter at much lower temperatures so that the post-treatments are significantly simplified, and residues of lower fluidity, including salts, are not formed, thus eliminating the necessity for supplying water for processing the residues separately. This also results in simplifying the post-treatment processes.
Also, since the process is carried out in one direction, there is no need for complex arrangement for circulating the mixture phase in the reaction chamber as in the conventional apparatus, so that the apparatus itself and controlling method of operation are significantly simplified.
The reaction chamber may be designed with a length at least four times higher than the diameter. Also, the reaction chamber may be made with a double-walled cylinder to form a thermal fluid passage surrounding the super-critical zone and/or the sub-critical zone. In such case, it is possible to generate a reaction field at elevated temperatures, higher than 600-650xc2x0 C., which are the usual limiting temperatures for metallic materials. Therefore, with the aid of combustion heat generated by an auxiliary fuel, it is possible to operate the apparatus continuously at temperatures in the range of 650-800xc2x0 C., exceeding thermal resistance temperature of metals.
The feed supply inlet may comprise a slurry supply nozzle for feeding a slurry or a liquid containing the object matter, and a medium supply inlet for feeding a medium at a temperature exceeding the critical temperature.
The super-critical zone may be provided with a tubular structure for forming a localized continuous reaction field. The tubular structure having one end opened to the feed supply inlet and other end opened towards downstream.
In a lower section of the reaction chamber, a tubular discharge section may be disposed transversely to the sub-critical zone. The discharge section may be constructed with a certain angle to horizontal direction and a gas outlet may be provided in an upper end.
The discharge section may be provided with a mechanical type transport device for moving the slurry phase. The transport device may comprise transport screws. The transport screws may comprise vanes disposed discontinuously about a shaft. The transport device may be connected to a drive source by way of a coupling section using a fluid sealing mechanism.
The thermal fluid fed at the thermal fluid passage may be a medium at a temperature less than the critical temperature of the medium. A part of the medium supplied to the thermal fluid passage can be heated to a temperature higher than the critical temperature, and delivered to the feed supply of the reaction chamber.
The apparatus may be provided with a scraping device for scraping objects adhering to and/or growing on the internal wall surface of the sub-critical zone in the reaction chamber or a stirring device for stirring a mixture phase.
A pre-treatment vessel at a sub-critical temperature may be further provided for pre-processing the object matter to be sent to the reaction chamber. The pre-treatment vessel may be provided with an outlet for discharging an object matter at substantially the same height of the feed supply inlet of the reaction chamber.
The apparatus may be provided with a cooling device downstream of the reaction chamber for further cooling the object matter and a separation tank for separating vapor/liquid from cooled object matter by subjecting the object matter to a reduced pressure. A pressure reducing device may be provided between the reaction chamber and the cooling device. The pressure reducing device may comprise at least two pressure reducing tanks separated by a middle valve. After filling a first tank with an object matter, the middle valve is opened and the object matter is expanded into a second tank in such a way to reduce pressure of the object matter. A heat exchanger may be provided to preheat the object matter using the gas phase produced in the separation tank.
This invention relates also to a method for performing the super-critical reactions by subjecting a mixture phase comprising an object matter and a medium to the super-critical temperature of the medium. The method comprises: a first step of producing a sub-critical state in the mixture phase in the absence of oxidizing agent; and a second step of producing the super-critical state in the presence of an added oxidizing agent.
After the second step, the method may further comprise a third step of producing a single liquid phase or a mixture phase containing a liquid phase and solid substances, or noncondensable gases, by cooling to the sub-critical temperature, and includes a step of withdrawing it from a reaction tower at a temperature less than the critical temperature. The second step may be carried out inside an inner wall held at a temperature less than the critical temperature.
The inner wall may be maintained at a temperature less than the critical temperature by flowing a fluid along an outer surface of the inner wall held at a pressure equal to, or substantially higher than a pressure of the object matter at less than the critical temperature.
The second step may be carried out inside the tubular structure for producing localized continuous reaction fields in the inner wall. The second step may also be carried out in a substantially vertical cylindrical reaction chamber comprising the upstream super-critical zone and the downstream sub-critical zone, and the object matter and reaction products are moved in one direction towards a lower end in the reaction chamber.
An object matter, an oxidizing agent and a medium at the super-critical temperature may be supplied to the super-critical zone in the reaction chamber. Here, oxidizing agents include oxygen-containing gases such as oxygen gas or air, or so-called oxidizers such as hydrogen peroxide.
The method may include a step of pre-liquefying the object matter, or may include a step of treating the object for becoming the pH value neutral or weakly acidic by adding acid or alkaline prior to processing. Also, a temperature higher than the critical point may be achieved by combustion reactions at the super-critical zone with the addition of auxiliary fuel to the object matter.
To prevent the separation of the object matter and the medium, a dispersant may be added to the object matter.
This invention also relates to a method for producing the super-critical reaction by subjecting a mixture phase containing an object matter and a medium to the super-critical state of the medium to carry out a reaction, and subjecting the mixture phase containing reaction products to a post-treatment in the sub-critical state.
This invention also relates to an apparatus for processing substances by subjecting a mixture phase, containing an object matter and a liquid medium, to the sub-critical state or the super-critical state. The apparatus has: a reaction chamber of a substantially vertical cylindrical shape with a feed supply inlet at an upper end and a product outlet at a lower end, and for forming a reaction zone in interior, wherein the object matter and reaction products are moved in one direction towards the lower end in the reaction zone formed in interior of the reaction chamber.
This invention also relates to an apparatus for processing substances by subjecting a mixture phase, containing an object matter and a liquid medium, to the sub-critical state or the super-critical state. The apparatus has: a reaction chamber of a substantially vertical cylindrical shape with a feed supply inlet at an upper end and a product outlet at a lower end, and a reaction zone formed in interior, wherein the reaction chamber is a double-walled cylinder comprising an inner sleeve and an outer sleeve to form a thermal fluid passage surrounding the reaction zone. The inner sleeve may be detachably installed, and may be assembled by insertion. Also, the liquid medium flowing through the thermal fluid passage may be a thermal fluid.
The reaction zone in the sub-critical state may include a vane section for scraping substances adhered to the inner wall and/or stirring a mixture phase. The vane section may have a sealing mechanism for retaining the medium under pressure around an area enclosing a shaft hole for inserting a drive shaft.
Oxidation reactions may be performed by using a medium in the sub-critical state in conjunction with any of the apparatuses disclosed above.
This invention also relates to a method for producing oxidation reactions by subjecting a mixture phase, containing an object matter and a liquid medium, to the sub-critical state of the medium. The method comprises: a first step of producing the sub-critical state in the mixture phase in an absence of oxidizing agent; and a second step of producing the super-critical state with an added oxidizing agent.